The present invention relates to a transmission that transmits a power of an engine to an axle shaft and, in particular to a transmission that can transmit a power of an engine to an axle shaft during a gear change.
At present, an AMT (Automated Manual Transmission) is available. The AMT has better fuel efficiency than an AT (Automatic Transmission) and is easier to operate than a MT (Manual Transmission). The AMT has almost the same structure as the traditional MT. In the AMT, a gear change (gear shift) and a clutch operation are implemented by a hydraulic actuator or an electric actuator in accordance with a signal from an ECU (electronic control unit), instead of a driver. According to the AMT, fuel efficiency can be improved.
Similarly to the MT, the ATM needs to disengage the clutch during a gear change operation. If the clutch is disengaged, a driving force is not transmitted from the engine to the axle shaft. For this reason, smooth drivability like the AT may not be achieved during a gear change operation.
In order to address this problem, a twin-clutch type of AMT having two clutches has been proposed. In the case of the twin-clutch AMT, one clutch is currently engaged. The other clutch is disengaged in preparation for traveling after the next gear change. A shaft of the other clutch is already connected to a gear to be selected in the next gear change. During the gear change operation, the current clutch is disengaged while the other clutch is engaged. Thus, the twin-clutch type AMT reduces the time period during which a driving force is not transmitted to the axle shaft, which implements better drivability like the AT.
However, the twin-clutch type AMT still has a problem that its weight is heavy and its size is large because it needs a complicated mechanism.
There is another approach for compensating for a driving force by using a motor connected to a driving wheel when a clutch is disengaged. However, this approach needs additional devices such as a motor and a battery, which increases the weight and size of the transmission.
Thus, in order to solve the above-described problems, it is an object of the present invention to provide a transmission that can continuously, without interruption, transmit a driving force over a gear change operation and that requires less increase in weight and size.